Driven roller, transport roller device, and liquid ejecting apparatus

ABSTRACT

A driven roller operates together with a driving roller to form a nip area for a medium to be transported. The driven roller includes a roller shaft and a roller element having a through hole through which the roller shaft extends. A contact position at which the roller shaft and an inner surface of the through hole are in contact with each other is located within the nip area.

BACKGROUND

1. Technical Field

The present invention relates to a driven roller that operates together with a driving roller to form a nip area for a medium to be transported. The invention also relates to a transport roller device including a driving roller, a driven roller that operates together with the driving roller to form a nip area for a medium to be transported, and a pressing-force applying unit that applies a relative pressing force between the driving roller and the driven roller. The invention also relates to a liquid ejecting apparatus including the transport roller device.

Here, the liquid ejecting apparatus is not limited to a recording apparatus, such as a printer, a copy machine, and a facsimile machine, which includes an ink jet recording head and performs recording on a recording medium by ejecting ink from the recording head. The liquid ejecting apparatus may also be an apparatus that ejects liquid corresponding to the use thereof instead of the ink. The liquid is ejected from a liquid ejecting head, which corresponds to the recording head, toward a medium corresponding to the recording medium so that the liquid adheres to the medium.

In addition to the recording head, a color-material ejecting head used for manufacturing a color filter of a liquid crystal display or the like, an electrode-material (conductive paste) ejecting head used for forming electrodes of an organic EL display, a field emitting display (FED) etc., a living-organic-material ejecting head used for manufacturing biochips, a sample-ejecting head that functions as a precision pipette, etc., may be used as a liquid ejecting head.

2. Related Art

FIGS. 8 and 9 illustrate the structure of a known transport roller device described in, for example, JP-A-2006-248688. Transport driven rollers 100 shown in FIG. 8 have a known structure in which two roller elements 103 are provided on a single roller shaft 101 with a gap therebetween in an axial direction. A pressing force is applied to an intermediate portion of the roller shaft 101 by a spring (not shown), as shown by the arrow 105. Thus, the transport driven rollers 100 are pressed against the transport driving roller 107. Nip areas 109 are formed by the pressing force as pressure contact sections between the rollers. A recording medium (not shown) is nipped in the nip areas 109 and receive a transporting force toward a recoding section as the transport driving roller 107 rotates.

The roller elements 103 have the known structure, and have through holes 111 through which the roller shaft 101 extends. As shown in FIG. 9, each of the through holes 111 has a large-diameter portion 113 and a small-diameter portion 115 due to manufacturing reasons. In each roller element 103, the inner surface of the small-diameter portion 115 is in contact with the outer surface of the roller shaft 101, and the inner surface of the large-diameter portion 113 faces the roller shaft 101 with a clearance therebetween. The two roller elements 103 are assembled such that the large-diameter portions 113 thereof are at the near ends and the small-diameter portions 115 thereof are at the far ends. In this structure, when the pressing force is applied at the position shown by the arrow 105 in FIG. 8, the pressing force is transmitted to the roller elements 103 through the roller shaft 101 so that the roller elements 103 receive the pressing force at points shown by the arrows 117 in the boundaries between the large-diameter portions 113 and the small-diameter portions 115. As a result, the roller elements 103 are pressed against the transport driving roller 107 and are rotated by the rotation of the transport driving roller 107.

In each roller element 103, the small-diameter portion 115 is in contact with the roller shaft 101 over the entire length thereof, and the contact area extends beyond the nip area. Therefore, the points at which the pressing force is applied when the roller elements 103 are rotated may be displaced from the boundaries shown by the arrows 117 and be moved within the entire length of the small-diameter portions 115 depending on the manufacturing accuracy and assembly accuracy. As a result, the outer surfaces of the roller elements 103 are slightly deformed and undulated while the roller elements 103 are being rotated. Accordingly, regions in which strong nipping force is applied and regions in which small nipping force is applied are generated in the nip areas. Consequently, the recording medium cannot be transported in a stable manner and the recording quality is reduced.

SUMMARY

An advantage of some aspects of the invention is that a driven roller, a transport roller device, and a liquid ejecting apparatus can be provided in which an area where a pressing force is applied by a roller shaft is restricted in a through hole formed in the driven roller so that a stable nipping force can be applied in a nip area and a recording medium can be transported in a stable manner.

According to a first aspect of the invention, a driven roller operates together with a driving roller to form a nip area for a medium to be transported. The driven roller includes a roller shaft and a roller element having a through hole through which the roller shaft extends. A contact position at which the roller shaft and an inner surface of the through hole are in contact with each other is located within the nip area.

According to the first aspect of the invention, the contact position at which the inner surface of the through hole formed in the roller element and the outer peripheral surface of the roller shaft are in contact with each other is located within the nip area formed by the driven roller for the medium to be transported. Since the contact position, at which the roller element receives a pressing force from the roller shaft, is within the nip area, the driven roller can be stably rotated and a stable nipping force can be applied in the nip area. As a result, the recording medium can be transported in a stable manner.

It is preferable that the driven roller have a convexly curved outer surface so that an outer circumference of the driven roller at the center thereof in an axial direction is larger than an outer circumference of the driven roller at ends thereof in the axial direction.

In such a case, since the driven roller has the convexly curved outer surface, that is, since the driven roller has a barrel-like shape, the nip area is formed on the outer surface of the driven roller in a region extending in an axial direction and including the position where the outer diameter of the driven roller is at a maximum. Since the contact position is located within the thus-formed nip area, the above-described effects of the first aspect of the invention can be enhanced.

In the driven roller, it is preferable that the contact position at which the roller shaft and the inner surface of the through hole are in contact with each other be located in a central area of the roller element in an axial direction.

In such a case, since the contact position at which the roller shaft and the inner surface of the through hole are in contact with each other is located in the central area of the roller element in the axial direction, the above-described effects can be further enhanced.

In the driven roller, it is preferable that the through hole have a small-diameter portion and a large-diameter portion and the small-diameter portion be at the contact position.

In such a case, since the through hole has the small-diameter portion and the large-diameter portion and the small-diameter portion is at the contact position, the contact position is limited within the area of the small-diameter portion. Therefore, the structure and the manufacturing process can be simplified. In addition, the driven roller can be stably rotated and a stable nipping force can be applied in the nip area. As a result, the recording medium can be transported in a stable manner.

In the driven roller, it is preferable that the through hole have a symmetrical shape in an axial direction about a central portion of the roller element.

In such a case, the pressing force applied in the nip area is balanced in the left-right direction with respect to the center in the nip area. Therefore, in addition to the above-described effects, an additional effect can be obtained that balanced, stable nipping force can be applied to the recording medium and the recording medium can be prevented from becoming skewed or wrinkled.

According to a second aspect of the invention, a transport roller device includes a driving roller; a driven roller that operates together with the driving roller to form a nip area for a medium to be transported; and a pressing-force applying unit that applies a relative pressing force between the driving roller and the driven roller. The driven roller includes a roller shaft and a roller element having a through hole through which the roller shaft extends. A contact position at which the roller shaft and an inner surface of the through hole are in contact with each other in the driven roller is located within the nip area.

According to the second aspect of the invention, the contact position at which the inner surface of the through hole formed in the roller element and the outer peripheral surface of the roller shaft are in contact with each other is located within the nip area formed between the driven roller and the driving roller for the medium to be transported. Since the contact position, at which the roller element receives a pressing force applied by the pressing-force applying unit from the roller shaft, is within the nip area, the driven roller can be stably rotated and a stable nipping force can be applied in the nip area. As a result, the recording medium can be transported in a stable manner.

In the transport roller device, it is preferable that the driven roller have a convexly curved outer surface so that an outer circumference of the driven roller at the center thereof in an axial direction is larger than an outer circumference of the driven roller at ends thereof in the axial direction. In such a case, effects similar to the above-described effects can be obtained.

In the transport roller device, it is preferable that the contact position at which the roller shaft and the inner surface of the through hole are in contact with each other be located in a central area of the roller element in an axial direction. In such a case, effects similar to the above-described effects can be obtained.

According to a third aspect of the invention, a liquid ejecting apparatus includes a transporting unit that transports a medium to be transported, a liquid ejecting unit that ejects liquid toward the medium, and an ejecting unit that ejects the medium after the liquid is ejected toward the medium. The transporting unit includes the above-described transport roller device. According to the third aspect of the invention, the medium can be stably transported to the liquid-ejecting unit. Therefore, high-quality liquid ejection and recording can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a sectional side view of an ink jet recording apparatus including a transport roller device according to an embodiment of the invention.

FIG. 2 is a perspective view illustrating a section around the transport roller device according to the embodiment of the invention.

FIG. 3 is a plan view illustrating the section around the transport roller device according to the embodiment of the invention.

FIG. 4 is a side view illustrating the state of a roller shaft included in a transport driven roller.

FIG. 5 is a partially sectioned front view illustrating the main part of a transport roller device according to a first embodiment of the invention.

FIG. 6 is a partially sectioned front view illustrating the main part of a transport roller device according to another embodiment of the invention.

FIGS. 7A and 7B are diagrams illustrating a difference in performance between a known transport roller and a transport roller according to an embodiment of the invention.

FIG. 8 is a partially sectioned front view of a portion of a known transport roller device illustrating a problem caused by the known transport roller device.

FIG. 9 is an enlarged sectional view of a known transport driven roller.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the invention will be described below with reference to the drawings. FIG. 1 is a sectional side view of an ink jet recording apparatus including a transport roller device according to an embodiment of the invention. FIG. 2 is a perspective view illustrating a section around the transport roller device according to the embodiment of the invention. FIG. 3 is a plan view illustrating the section around the transport roller device according to the embodiment of the invention. FIG. 4 is a side view illustrating the state of a roller shaft included in a transport driven roller. FIG. 5 is a partially sectioned front view illustrating the main part of a transport roller device according to a first embodiment of the invention.

First, the schematic structure of an ink jet recording apparatus 1 (hereinafter simply called a recording apparatus), which serves as a liquid ejecting apparatus according to an embodiment of the invention, will be described with reference to FIGS. 1 to 4. The recording apparatus 1 includes a feeding device 3 for feeding recording media P, which is an example of media to be transported. The recording medium P at the top of the stack in the feeding device 3 is pressed against the outer peripheral surface of a feeding roller 7 by a hopper 9 that pivots toward the feeding roller 7. As the feeding roller 7 is rotated, the recording media P are automatically fed one at a time toward a transport roller device 11. The transport roller device 11 includes a transport driving roller 13 disposed at a lower position and transport driven rollers 15 disposed at upper positions.

A carriage 19 that reciprocates a recording head 17 relative to the recording medium P in a medium width direction is disposed downstream of the transport roller device 11. The recording head 17 performs recording on the recording medium P by ejecting ink toward the recording medium P. The carriage 19 carries ink cartridges (not shown) containing inks of different colors, and the inks are supplied to the recording head 17 from the respective ink cartridges. The recording head 17 reciprocates in the medium width direction at a position where the recording head 17 faces a platen 21, and has a plurality of nozzles (not shown) in a head surface thereof.

The recording medium P is transported on the platen 21 at an accurate pitch by a driving force applied by the transport roller device 11. At the same time, a desired recording operation is performed by ejecting ink toward the recording medium P from the nozzles. After the recording operation, the recording medium P is ejected by an ejection roller unit 23 including an ejection driving roller 25 and an ejection driven roller 27.

First Embodiment

The characteristic structure of the transport roller device 11 according to a first embodiment of the invention will be described below. In the first embodiment, as shown in FIGS. 2 and 3, the transport roller device 11 includes a single, long transport driving roller 13 and four transport driven rollers 15. The transport driven rollers 15 are divided into two pairs of transport driven rollers 15 that are arranged in series. In each pair, two transport driven rollers 15 are disposed on a single roller shaft 29 with a gap provided therebetween in an intermediate section 31 of the roller shaft 29. Each of the roller shafts 29 is retained by bearings 33 at both ends thereof. However, as shown in FIG. 4, the outer peripheral surface of each transport driven roller 15 is supported by the outer peripheral surface of the transport driving roller 13, so that the bearings 33 do not support the roller shafts 29 but restrain the movement of the roller shafts 29 in the front-rear direction.

In the intermediate section 31 between each pair of the transport driven rollers 15, the roller shaft 29 is pressed from above by an end portion 37 at an end of a torsion spring 35 while an end portion 39 at the other end of the torsion spring 35 is fixed to a structural member of the recording apparatus 1. Bearings 41 are provided at the intermediate sections 31. However, similar to the bearings 33 at the edges of the roller shafts 29, the bearings 41 simply restrain the movement of the roller shafts 29 in the front-rear direction.

As shown in FIG. 5, each of the transport driven rollers 15 has a convexly curved outer surface so that the outer circumference at the center is slightly larger than the outer circumference at the ends. In other words, each transport driven roller 15 has a barrel-like shape. Nip areas 43 in which the recording medium P can be nipped are formed between the transport driving roller 13 and the transport driven rollers 15. The nip areas 43 are formed on the outer peripheral surface of the transport driving roller 13 in regions extending in the axial direction and including the positions where the outer diameters of the respective driven rollers 15 are at a maximum. The recording medium P is nipped between the transport driving roller 13 and the transport driven rollers 15 in the nip areas 43, and is transported toward the recording head 17 by the driving force applied by the transport driving roller 13.

Each transport driven roller 15 has a roller element 45 that rotates together with the corresponding roller shaft 29. Each roller element 45 has a through hole 47 through which the roller shaft 29 extends. Each through hole 47 has large-diameter portions 49 at the ends of the roller element 45 and a small-diameter portion 51 disposed between the large-diameter portions 49. Thus, in each roller element 45, the small-diameter portion 51, at which the inner surface of the through hole 47 comes into contact with the roller shaft 29, is positioned at the center of the roller element 45 in the axial direction thereof. The outer diameter of each roller shaft 29 is set such that the roller elements 45 can come into contact with the peripheral surface of the roller shaft 29 in the small-diameter portions 51 and such that the roller elements 45 can rotate together with the roller shaft 29. In the state in which the transport driven rollers 15 are pressed against the transport driving roller 13, each roller shaft 29 is in contact with the roller elements 45 only in areas where the small-diameter portions 51 are formed. Therefore, the pressing force N applied to the roller shafts 29 by the torsion springs 35 is transmitted to the roller elements 45 through the small-diameter portions 51 positioned at the centers of the transport driven rollers 15.

As shown in FIG. 5, each small-diameter portion 51 has a length smaller than that of each nip area 43, and is positioned within the corresponding nip area 43. Therefore, all of the pressing force transmitted to the roller elements 45 through the small-diameter portions 51 is applied in the nip areas 43. Thus, the force applied to the roller shafts 29 by the torsion springs 35 is not applied in areas outside the small-diameter portions 51. As a result, unlike the known structure in which the outer surfaces of the roller elements 103 (FIG. 8) are undulated while the roller elements 103 are being rotated, the recording medium can be transported in a stable manner.

In the present embodiment, each through hole 47 has a symmetrical shape in the axial direction about the center of the roller element 45. Therefore, the force applied to the nip areas 43 through the small-diameter portions 51 is balanced in the left-right direction with respect to the center in each nip area 43. As a result, a stable nipping force is applied to the recording medium P and the recording medium P is prevented from becoming skewed or wrinkled.

Next, effects obtained by the transport roller device according to the invention will be described below with reference to FIGS. 7A and 7B. FIGS. 7A and 7B show pressure distributions on the recording medium P when the transport driven rollers are rotated. Dark regions show areas there high pressure is applied. Referring to FIG. 7A, with the known transport driven rollers 100, distinct dark and light regions are formed periodically as the transport driven rollers 100 rotate. It is clear that the regions in which the pressure is applied are moved in the axial direction of the transport driven rollers 100.

In comparison, as shown in FIG. 7B, with the transport driven rollers 15 according to the embodiment of the invention, dark and light regions formed as the transport driven rollers 15 are rotated are not as distinct as those in FIG. 7A. In addition, the pressure distribution is relatively even in both the peripheral direction and the axial direction of the transport driven rollers 15. Therefore, in the transport roller device 11 according to the embodiment of the invention, the nipping force hardly varies in the peripheral direction and in axial direction and the recording medium can be transported in a stable manner.

Other Embodiments

FIG. 6 is a partially sectioned front view illustrating the main part of a transport roller device according to another embodiment of the invention. In this transport roller device, pressing force is applied at three positions.

In the first embodiment, the pressing force is applied at one position, that is, at the intermediate section 31, for each pair of the transport driven rollers 15. In this embodiment, as shown in FIG. 6, the pressing force N is applied not only at the intermediate section 31 but also at the ends of the roller shaft 29. Other structures are the same as those of the first embodiment. Components similar to those of the first embodiment are denoted by the same reference numerals, and explanations thereof are thus omitted. The effects similar to those of the first embodiment can also be obtained by this structure.

In the above-described embodiments, two transport rollers 15 are provided on each roller shaft 29. However, three or more transport driven rollers 15 may also be provided on a single roller shaft 29. In such a case, the positions of the small-diameter portions 51 of the transport driven rollers 15, that is, the contact positions between the roller shaft 29 and the inner surface of the through hole 47, are positioned in the respective nip areas 43.

Although the ink jet recording apparatus is described above as an example, the transport roller device according to an embodiment of the invention can also be used in other kinds of liquid ejecting apparatuses. For example, the transport roller device may be used in a liquid ejecting apparatus that ejects liquid corresponding to the use thereof instead of the ink. The liquid is ejected from a liquid ejecting head, which corresponds to the recording head, toward a medium (medium to be transported) corresponding to the recording medium so that the liquid adheres to the medium.

The entire disclosure of Japanese Patent Application No. 2007-105968, filed Apr. 13, 2007 is expressly incorporated by reference herein. 

1. A driven roller that operates together with a driving roller to form a nip area for a medium to be transported, the driven roller comprising: a roller shaft; and a roller element having a through hole through which the roller shaft extends, wherein a contact position at which the roller shaft and an inner surface of the through hole are in contact with each other is located within the nip area.
 2. The driven roller according to claim 1, wherein the driven roller has a convexly curved outer surface so that an outer circumference of the driven roller at the center thereof in an axial direction is larger than an outer circumference of the driven roller at ends thereof in the axial direction.
 3. The driven roller according to claim 1, wherein the contact position at which the roller shaft and the inner surface of the through hole are in contact with each other is located in a central area of the roller element in an axial direction.
 4. The driven roller according to claim 1, wherein the through hole has a small-diameter portion and a large-diameter portion, and the small-diameter portion is at the contact position.
 5. The driven roller according to claim 4, wherein the through hole has a symmetrical shape in an axial direction about a central portion of the roller element.
 6. A transport roller device, comprising: a driving roller; a driven roller that operates together with the driving roller to form a nip area for a medium to be transported; and a pressing-force applying unit that applies a relative pressing force between the driving roller and the driven roller, wherein the driven roller includes a roller shaft, and a roller element having a through hole through which the roller shaft extends, wherein a contact position at which the roller shaft and an inner surface of the through hole are in contact with each other in the driven roller is located within the nip area.
 7. The transport roller device according to claim 6, wherein the driven roller has a convexly curved outer surface so that an outer circumference of the driven roller at the center thereof in an axial direction is larger than an outer circumference of the driven roller at ends thereof in the axial direction.
 8. The transport roller device according to claim 6, wherein the contact position at which the roller shaft and the inner surface of the through hole are in contact with each other is located in a central area of the roller element in an axial direction.
 9. A liquid ejecting apparatus, comprising: a transporting unit that transports a medium to be transported; a liquid ejecting unit that ejects liquid toward the medium; and an ejecting unit that ejects the medium after the liquid is ejected toward the medium, wherein the transporting unit includes the transport roller device according to claim
 6. 